OpenwebUI integration

[grimwiz]

Here is how to tie the dice roller into OpenwebUI as a tool.

##Example output:

Q. dice roller 4d6 discard lowest
A. Thought for less than a second
You rolled a 3, 5, 6 and a 1.
Discard the lowest (the 1) and sum the rest: 3 + 5 + 6 = 14.

##Files

Dockerfile:

FROM node:22-slim

WORKDIR /app

# Install CLI version of dice roller
RUN npm install --production @dice-roller/cli express

# Copy server
COPY server.mjs .

USER node
EXPOSE 8000

CMD ["node", "server.mjs"]

file: server.mjs

import express from "express";
import { DiceRoll } from "@dice-roller/rpg-dice-roller";

const app = express();
app.use(express.json());

// OpenAPI spec so OpenWebUI knows how to call this tool
const openapiSpec = {
  openapi: "3.0.1",
  info: {
    title: "Dice Roller API",
    version: "1.0.0"
  },
  paths: {
    "/dice": {
      post: {
        summary: "Roll dice",
        operationId: "Dice",   // MUST match what OpenWebUI expects
        requestBody: {
          required: true,
          content: {
            "application/json": {
              schema: {
                type: "object",
                properties: {
                  dice: {
                    oneOf: [
                      { type: "string" },
                      { type: "array", items: { type: "string" } }
                    ]
                  },
                  roll: {
                    oneOf: [
                      { type: "string" },
                      { type: "array", items: { type: "string" } }
                    ]
                  },
                  formula: { type: "string" }
                },
                example: { dice: "3d6" }
              }
            }
          }
        },
        responses: {
          "200": {
            description: "Dice roll result",
            content: {
              "application/json": {
                schema: {
                  type: "object",
                  properties: {
                    result: { type: "string" }
                  }
                }
              }
            }
          }
        }
      }
    }
  }
};

// Serve the OpenAPI spec (GET and POST supported)
app.get("/openapi.json", (req, res) => {
  res.json(openapiSpec);
});

app.post("/openapi.json", (req, res) => {
  res.json(openapiSpec);
});

// Handle dice rolls
app.post("/dice", (req, res) => {
  console.log("Incoming request body:", req.body);

  let formula =
    req.body.formula ||
    req.body.dice ||
    req.body.roll;

  if (Array.isArray(formula)) {
    formula = formula.join(" ");
  }

  if (!formula) {
    return res.status(400).json({ error: "Missing dice formula" });
  }

  try {
    const roll = new DiceRoll(formula);
    res.json({ result: roll.output });
  } catch (err) {
    res.status(400).json({ error: err.message });
  }
});

const PORT = process.env.PORT || 8000;
app.listen(PORT, () => {
  console.log(`Dice Roller API running on port ${PORT}`);
});

Fragment of docker-compose.yaml (add it as a stanza to your other openapi docker tools)

  dice-roller:
    build:
      context: ./dice-roller-mcp-docker
      dockerfile: Dockerfile
    container_name: dice-roller
    ports:
      - "8085:8000"
    restart: unless-stopped
    user: "1000:1000"
    security_opt:
      - no-new-privileges:true
    cap_drop:
      - ALL
    mem_limit: 256m
    cpus: "0.5"

In OpenwebUI's configuration, using the address of the docker server and the port listed in the fragment above add the tool.

[grimwiz]

Under Workspace -> Models you can create a dice-aware model by turning on the "Dice Roller" tool there.